Revert "Revert "改进 Upyun 初始化，将少连接的过程;""

This reverts commit 370aec45db3f764e44f436df39d1e995b0da2df2.
Update lib/carrierwave/storage/upyun.rb

解决 “改进 Upyun 初始化，减少连接的过程” 中bucket混乱的问题
属于issue #16